Method of making abrasive articles



Patented July 23, 1946 STAT-ES METHOD OF MAKING ABRASIVE ARTICLES JuliusF. Sachse, Summit, N. J., assignor to Metals Disintegrating Company,Inc., Elizabet N. J a Corporation of New Jersey I No Drawing.Application August 23, 1944,

V I Serial No.550,862

' 1Claim. (Cl.51 293) This invention relates to powder metallurgy and tothe manufacture of metal bodies in which minute grains of nonmetallicabrasive materials are uniformly distributed. Such metallic bodies havemany fields of use, including cutting or lapping wheels or stones,friction surfaces used as treads, brake linings, clutch facingsand thelike, and wear-resisting surfaces of all kinds. In such uses themetallic portion of the body may perform as a structural member orcontribute functions closely allied to the use to which the body isplaced, but in every case the metal serves as a matric in which theabrasive is imbedded and held. Often it is only necessary to form a thinsurfacing of such a metal-abrasive body, Sometimes, and particularlywhere the surface may wear away with us, it is desirable that themetal-abrasive body be of substantial depth. However, regardless of theuse, it is always desirable that the grains of nonmetallic abrasive beuniformly distributed throughout the metal matrix and securely bondedthereto and that these grains be, within practical limits, of uniformsize and quality so that the metal-abrasivebody may always present asurface of uniform characteristics.

It is lack of uniformity of the friction, cutting or wearing surfacepresented by these metalabrasive bodies and the readiness with which theabrasive grain is removed from the matrix which has been the greatestobstacle to their widespread use and low cost production, and it is theobject of this invention to provide a method by which the components ofsuch bodies may be manufactured.

Previously the art has used two general methods of making metal bodieswhich embody therein distributed grains of nonmetallic abrasives. One ofthese methods is based upon casting the molten metal around or on theabrasive grains or, alternatively, mixing the abrasive grains with themolten metal prior to casting. The other, and more flexible, methodconsists in forming the mixture of abrasive grains and particles ofmetal powder and compressing and molding this mixture into a body of thedesired shape, in ac cordance with the well known practices used for themolding of metal powders. All such methods possess, in greater or lesserdegree, the common fault of non-uniformity of product and insecurebonding of abrasive and matrix. This lack of uniformity is caused inpart, and perhaps in greater part, by the diil'erences in densitybetween the nonmetallic abrasives and the metal and, in part, by thedifficulties encountered in physically handling and mixing relativelyfine sized granular materials and by the insecurity of bonding that isinherent in this method. The present invention relates to those methodsof forming metal-abrasive bodies in which the body is constructed bymolding and compacting metal powder, and is predicated on a method ofmaking a product to be used for this purpose, which product consists ofmetal powder the particles of which have nonmetallic abrasivegrains'attached to their. surfaces, the sizeof thesegrains being of theorder of about 1 to 25 microns. This product may be molded by the knownpowder metal lurgy methods into bodies of proper size and shape and,when so molded, forms a body having a wear-resisting friction orabrasive surface that is not only uniform from the standpoint ofdistribution of abrasive therein but is also uniform in the sense thatthe abrasive particles are of even size or are so minute in size thatvariation thereof is unimportant to many uses to which thesemetal-abrasive bodies may be put.- It is further characterized by theintegrity of, bond. between the abrasive grains and the metallic matrix.V v

The nonmetallic abrasives to which reference is herein made are themetallicoxides which have, for-the purpose of the particular usecontemplated, abrasive, cutting, lapping, polishing, wear-resisting orfriction producing properties. As is well known, the commoncharacteristic of such oxides is a hardness greater than that of themetals. Common examples are aluminum oxide, silicon oxide and magnesiumoxide. Other less used oxide abrasives are zirconium dioxide, boronsesqui oxide and titanium dioxide. This listing is not inclusive butrepresents the more practical substances.

In the practice of this invention, I first select the desired abrasiveand the desired base metal in which the abrasive is to be imbedded,because,

as will hereinafter appear, the base metal must be one, the oxide ofwhich is reducible by reducing gases, such as hydrogen, at a lowertemperature than is the oxide which composes the abrasive. A furtherrequirement is that the matrix metal and the abrasive forming metal mustbe soluble in each other in the molten state in the proportionsnecessitated by the contemplated analysis of finished product. Thus, forinstance, if aluminum oxide is the abrasive contemplated, a matrix maybe selected from the metals set forth in List A. If silicon oxide is theabrasive selected, the matrix metal may be selected from 3 List B. As afurther example, if magnesium Oxide is the abrasive desired, the matrixmetal may be selected from List C.

List A List B List Zinc Iron Zinc Tin Nickel Nickel Iron Cobalt CopperNickel Copper Cobalt Copper In each case the metals listed are metalsthe oxide of which is more easily reduced by reducing gas than is theoxide which forms the abrasive to which the list refers. elusive ofmetals not named and contain only the commoner and more usable matrixmetals. Available standard data, or simple trial, may be used todetermine whether a non-listed metal forms an oxide more easilyreducible than the oxide from which the contemplated abrasive is made.In the practice of my invention, assuming the proper selection ofabrasive and matrix metal has been made, the metal whose oxide forms theabrasive and the metal which is to form the matrix are alloyed togetherin such proportions that the conversion of the abrasive forming metal tothe abrasive oxide will furnish in the final mixture the amount ofabrasive required. The thus proportioned alloy is then reduced to theform of a powder by any well known disintegrating process, such asatomizing, pulverizing or the like. The disintegrated alloy is thenheated to an elevated temperature, but below a temperature which wouldfuse the alloy sufliciently to destroy its powder form, and is subjectedto the action of an oxidizing gas, such as, for example, air or oxygen,thus causing oxidation of the abrasive forming metal to the desiredabrasive oxide, as well as causing oxidation of at least some of thebase metal. As soon as this oxidation reaction is complete, to the ex--tent that the desired quantity of abrasive oxide is formed, thetreatment with the oxidizing gas is terminated and the product of thistreatment is. reacted with the gaseous reducing agent, such as hydrogenor the like, to cause reduction of such oxide of the matrix metal as hasbeen formed These lists are not exmatrix oxide. In the practice of myinvention the product of the oxidizing step is usually in the form of acake, and it is sometimes necessary or desirable that the oxidizedproduct be cooled and pulverized before being submitted to the reducingtreatment. The product produced by the final reduction step is cooledunder conditions which do not admit of further oxidation, pulverized andscreened, and the result is a metal powder, to the particles of whichare attached grains of abrasive oxide, said grains being usually of verysmall size, in the order of about 1 to 25 microns.

As a specific example of my method of producing such product may becited the preparation of a nickel powder bearing on its surface aluminumoxide grains. In this particular example a product containing 25 percent. A1203 and per cent. nickel was desired. Therefore, 84.9 parts ofnickel and 15.1 parts of aluminum were alloyed, atomized and screened tothe desired size. The powdered alloy was then heated to a temperature ofabout 1200" C. in a stream of air for about 4 hours. Thereafter theproduct was cooled, pulverized and reheated to a temperature of about800 C. and treated in a stream of hydrogen for about 2 hours. Thereafterthe product was cooled under hydrogen, pulverized and screened. Theresulting powdered product contained in mass about 25 per cent. A1203,the balance beingnickel with only traces of nickel oxide. The productconsisted of minute particles of metal powder to which were attachedvery small particles of aluminum oxide. This product, when molded intoproper shape and compressed under pressures of about 40,000 pounds persquare inch formed a metal-abrasive body in which the abrasive grainswere uniformly distributed.

Having thus described my invention, I claim:

In a method of making a metal powder product having grains of metaloxide abrasive attached to particles of said powder, comprisingselecting metal from which abrasive oxide is to be formed, selecting areducing gas, selecting as a powder metal a metal the oxide of which isreduced by said gas at a lower temperature than is said metal oxideabrasive, forming an alloy of said selected metal, placing said alloy inpowder form, subjecting said alloy to an oxidizing gas and then treatingthe oxidized alloy powder in said reducing gas at a temperature at Whichthe oxide of said powder metal is reduced but below the temperature atwhich the said abrasive metal oxide is reduced.

JULIUS F. SACHSE.

